Charity Navigator should make this an informal rule: If your charity is employing Sidney Blumenthal, it automatically goes on the watch list.

The ethical controversies around Hillary Clinton and the Clinton Foundation have often seemed 1990s redux, and never more so than when a New York Times story resurfaced longtime Clinton loyalist Blumenthal.

According to the Times, from a perch at the Clinton Foundation, Blumenthal was sending Secretary of State Hillary Clinton memos on Libya that she forwarded around the State Department, even though they were occasion for eye-rolling by the professionals.

Sidney Blumenthal is the former writer for The New Republic, The Washington Post and The New Yorker whose devotion to the Clintons was too much even for his fellow journalists.

He eventually traded in his status as a quasi-Clinton apparatchik for official Clinton apparatchik, taking a job at the White House.

He was noted for his conspiratorial thinking and nasty, highly personalized, whisper-campaign politics. Much can be learned about his smash-mouth style by studying the social behavior of the spotted hyena.

Ultimately, Blumenthal himself isn’t the issue. What’s interesting isn’t the suckerfish per se, but what it tells us about the shark.

When the Obama team went with Hillary Clinton as secretary of state, it undertook a high-stakes experiment: Could it hire a Clinton and, with enough rules and constraints, force him or her to act in a manner above reproach?

The Blumenthal affair is yet another indication that the answer is a resounding “no.”

Then-White House chief of staff Rahm Emanuel reportedly had Blumenthal banned for — what else? — spreading harsh attacks about Barack Obama during the 2008 primaries.

Emanuel’s edict would have seemed to bar Blumenthal from serving Clinton while she was secretary of state. Ah, but as the poet said, you can drive nature out with a pitchfork, she will nevertheless come back.

Blumenthal happened to be sending Hillary memos about Libya at the same time that he was in league with people trying to make money in Libya. Let’s think about this.

One scenario is that Blumenthal’s would-be business associates got together and thought: “We need to find the best expert we can on North Africa, someone who understands the subtleties of Libyan political and tribal dynamics. Let’s get Sidney Blumenthal!”

Another is that they thought: “We need to find someone who is in tight with the Clintons and has a back channel to Hillary so, when the time comes, the State Department will give our venture the most favorable possible consideration. Let’s get Sidney Blumenthal!”

The Blumenthal story underlines what we already knew or suspected about Hillary’s tenure as secretary of state and at the Clinton Foundation.

She portrays herself as the picture of openness, explaining how she wants her e-mails public as soon as possible. But we wouldn’t know about the Clinton-Blumenthal correspondence but for the exertions of a Romanian hacker.

For all its good works, the Clinton Foundation was a political slush fund and holding tank for Clinton operatives. Presumably, the March of Dimes manages to get along without paying former government officials as they scheme to return to power.

The ethics of Clinton’s tenure as secretary of state were atrocious. In what world is it OK for the secretary of state to get and pass along back-channel advice from a friend about a country where he has business interests at stake?

Finally, it’s impossible to credit “the new Hillary” so long as she is dependent on the same old cronies.

Asked about Blumenthal, Hillary said his e-mails were her effort to make sure she wasn’t “caught in the bubble.” Because nothing keeps you intellectually fresh and on your toes like e-mails from a loyal hatchet man of some 20 years and counting.